Iron is a critical nutritional element essential for a great variety of important biological processes including cell growth and differentiation, electron transfer reactions, and oxygen transport, activation, and detoxification. Also, increasing recent attention has focused on the role of iron in regulating gene expression. Iron regulation of gene expression occurs in bacteria, plants, yeast, and mammals including humans. This function of iron may provide a basis for further understanding the iron requirements of cell proliferation and differentiation. Although iron- responsive post-transcriptional gene regulation has been well described, transcriptional regulation by iron has been less well studied. Our laboratory has recently delineated a novel iron-dependent system of transcriptional regulation. At least two eukaryotic genes, protein kinase C-beta and tartrate resistant acid phosphatase/uteroferrin, are transcriptionally active in the presence of Fe (III) presented as ferric transferrin (FeTF), whereas both are inhibited at the transcriptional level in the presence of exogenous hemin (ferric protoporphyrin IX). It is now proposed to build upon these observations to identify additional genes whose expression is regulated by iron or hemin and to examine the roles of the products of iron/hemin regulated genes in hematopoietic cell proliferation and differentiation. The following specific aims are proposed: (1) to study the roles of the hTRAP and hPKC-beta genes, prototype iron/hemin responsive genes, in hematopoiesis; (2) to test the possibility that other mammalian genes with candidate hemin regulatory motifs may also be regulated by iron and hemin; (3) to identify by PCR differential hybridization screening )PDHS) and/or differential display PCR (DDRT-PCR) new hematopoietic cell genes which are activated or suppressed by iron or hemin and to determine their roles in hematopoietic cell differentiation; (4) to express the cloned genes identified in Aim 3 in a bacterial expression system and to examine effects of the purified, recombinant proteins on hematopoietic cell differentiation. Identification of a group of genes regulated at the transcriptional level by iron and hemin and elucidation of the possible functions of these genes in hematopoiesis will provide a basis for an expanded understanding of iron and related compounds in cellular homeostasis and should open new avenues for investigation in iron research.